1. Field of the Invention
The present invention relates to a method of manufacturing a lithium ion conductive solid electrolyte that is used for a lithium-ion secondary battery or the like and a lithium-ion secondary battery including such a lithium ion conductive solid electrolyte.
2. Description of the Related Art
Lithium-ion secondary batteries are used as small size drive power supplies with a high capacity for various fields such as automobiles, personal computers, mobile phones or the like.
Currently, as an electrolyte of the lithium-ion secondary battery, a liquid electrolyte of organic solvent such as ethylene carbonate, diethyl carbonate and methylethyl carbonate is used. However, generally, as such a liquid electrolyte of organic solvent is flammable, there may be problem of safety in a current lithium-ion secondary battery. Further, the liquid electrolyte of organic solvent has a limit in withstand voltage and if a high voltage is applied, there may be a case that the electrolyte is decomposed or altered.
With such a background, applying of inorganic solid electrolytes that are nonflammable and have a high stability against applied voltage is expected as electrolytes for lithium-ion secondary batteries of a next generation.
However, generally, such an inorganic solid electrolyte has a tendency that lithium ion conductivity is not so good compared with a liquid electrolyte at room temperature. Thus, in the present circumstances, lithium-ion secondary batteries using the inorganic solid electrolyte are used only for some products such as a thin small-size battery mounted on a pacemaker or the like.
Here, in order to cope with such a problem of the inorganic solid electrolyte, a method is proposed in which glass including monovalent ions whose ionic radii are larger than those of lithium ions is performed with an ion-exchange process in lithium ions contained in molten salt so that the monovalent ions are substituted for by the lithium ions by the ion-exchange process (Patent Document 1).